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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 34, issue 11
Ann. Geophys., 34, 1019-1030, 2016
https://doi.org/10.5194/angeo-34-1019-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: The 14th International Symposium on Equatorial Aeronomy

Ann. Geophys., 34, 1019-1030, 2016
https://doi.org/10.5194/angeo-34-1019-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 16 Nov 2016

Regular paper | 16 Nov 2016

Electrodynamic influence on the diurnal behaviour of neutral daytime airglow emissions

Deepak K. Karan1,2, Duggirala Pallamraju1, Kedar A. Phadke1, Tatiparti Vijayalakshmi3, Tarun K. Pant4, and Shyamoli Mukherjee5 Deepak K. Karan et al.
  • 1Physical Research Laboratory, Navrangpura, Ahmedabad, India
  • 2Indian Institute of Technology, Gandhinagar, Ahmedabad, India
  • 3Jawaharlal Nehru Technological University, Kukatpally, Hyderabad, India
  • 4Space Physics Laboratory, Trivandrum, India
  • 5Indian Institute of Geomagnetism, Navi Mumbai, India

Abstract. The diurnal variations in daytime airglow emission intensity measurements at three wavelengths OI 777.4nm, OI 630.0nm, and OI 557.7nm made from a low-latitude location, Hyderabad (17.5°N, 78.4°E; 8.9°N MLAT) in India have been investigated. The intensity patterns showed both symmetric and asymmetric behaviour in their respective diurnal emission variability with respect to local noon. The asymmetric diurnal behaviour is not expected considering the photochemical nature of the production mechanisms. The reason for this observed asymmetric diurnal behaviour has been found to be predominantly the temporal variation in the equatorial electrodynamics. The plasma that is transported across latitudes due to the action of varying electric field strengths over the magnetic equator in the daytime contributes to the asymmetric diurnal behaviour in the neutral daytime airglow emissions. Independent magnetic and radio measurements support this finding. It is also noted that this asymmetric diurnal behaviour in the neutral emission intensities has a solar cycle dependence with a greater number of days during high solar activity period showing asymmetric diurnal behaviour compared to those during a low solar activity epoch. These intensity variations over a long timescale demonstrate that the daytime neutral optical emissions are extremely sensitive to the changes in the eastward electric field over low and equatorial latitudes.

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Dayglow emission variability is expected to show a symmetric solar zenith-angle-dependent diurnal pattern as the production mechanisms are dominated by solar flux; however, this is not always the case. Our investigation reveals an imprint of equatorial electrodynamics on the neutral dayglow emission variability, as opposed to that of the solar zenith angle. This has implications in gaining a comprehensive understanding of the coupled nature of the ion-neutral behaviour in the upper atmosphere.
Dayglow emission variability is expected to show a symmetric solar zenith-angle-dependent...
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